I am departing on a 6 month backpack trip across Europe in September. The first 3 months will be on an unlimited eurail pass, the second will be fewer places for longer stays.I am a pretty laid back traveler and trust things will work out once I arrive so my greatest concern about planning this trip has been choosing the right gear.

I would like feedback on lens choices and I would LOVE advice on devices/methods for storing and editing photos(/video which i'm new to) for long trips. Cost is definitely a factor but am willing to make some investments.

I own:
70D
Sigma 20mm 1.8
Canon 50mm 1.8
A big laptop that is about to die and I use lightroom only for editing
External hard drive

Thinking of buying:
Sigma 18-35mm
Canon 85mm f 1.8
Tablet of some variety...I don't know anything about these. I do know for around $800 I could get laptop power in tablet size but I don't know if I need that.
I also don't have an unlimited budget and this set up would be tough to swing.

If I did that I would be bringing: 70D + 18-35mm + 35mm + some kind of tablet

I'm becoming more passionate about photography and am willing to invest some money into gear so that I wont have regrets looking back at photos of my journeys. When I was in India I was new to photography and had a super old wide angle (my dad's form his young days in photography...it is a crap lens) and my 50mm. I managed well with what I had but I wish so badly I had good gear to do the photos justice! (hence now having a 20mm)

I've wanted to add a semi telephoto to my collection and my 20mm is beautiful but does have flare that I don't particularly want following me in Europe.At the moment I am thinking of selling my 20mm and getting the Sigma 18-35 1.8 and get a 85mm (likely the Canon f1.8) and I would leave my 50mm at home.
I used a sling shoulder camera strap that I adore. I don't want to bring a camera specific bag as I like being more discrete. I think I'll make foam inserts that can be used in any regular packs. I've never owned a zoom, and have only shot prime.

and please please please...HOW do you guys store, backup, edit and upload photos while traveling? Do I need to let go of having the ability to edit and blog while on the go?
I'll need a tablet regardless as I refuse to bring my laptop and my smartphone (iphone 4) is also starting to die on me. If you have specific models, brands etc. I would love to hear. I ideally wouldn't be spending $800. I would really love to be able to blog on the go and am not clear on how much I need to spend to be able to do this.

Regarding tablets, I've had a series of iPads since they came out. I like them. But there are real liabilities for photographers in trying to rely on them for photo storage and processing. I much prefer my tiny 11" Macbook Air for travel, since it has more storage, a real keyboard, can run real photography software, and can attach to a small external drive for backups.

I'll hold off on addressing most of your camera questions for right now except to point out that small and light is good, and if you can afford it think about a small mirrorless setup. That's what I use when I travel.

I agree with Dan on the laptop, instead of a tablet, for the same reasons as he mentioned.

We just got back from England and France. I took my 70D and an 18-35mm f1.8, along with my 70-200mm f2.8.
Never even took the 70-200 out of the bag! We also have a G10 that we use when we don't want to take the 70D, which wasn't very often.

For small travel laptop/tablet devices, assuming you have windows applications, take a look at the Lenovo Yoga series. I have the Yoga 11s. Small and lightweight, real keyboard, touchscreen, sd card for expandable storage, usb 3.0 for external hard drive. The foldable screen is very useful and not a gimmick. I'm a big fan. They run Windows 8, and as much as some people really dislike Windows 8, I think it works well for touchscreen devices, and it has the advantage that it can regular windows applications like Lightroom with no problem. I like the hybrid devices. If I was buying new today, I'd also consider the Surface Pro 3 for the higher resolution screen and mini-displayport for connecting to a high-res external monitor at home.

I don't have any of the gear you mention except the 85 1.8. Really nice lens for sure. Would probably be a good combo with your 50mm and 18-35mm. I'll refrain from commenting on the rest. I've traveled with 2.8 lenses before, and that gets heavy, and I would also consider going high quality mirrorless in the future.

I spent 2 and a half months in Europe and on a boat in the Mediterranean.

I would highly recommend a 15-85mm, or 17-85mm. Maybe even an 18-200mm, although I always wonder about the IQ on those types of lenses. Something with a little bit of range. With the kit lens and the nifty 50mm there were times I wanted a little extra reach. That is really up to your shooting style. I am mostly looking at 15-30mm or 50-85mm when walking around.

Get two 500gb or 1tb hard drives. I did not have an issue and only brought 1 external hard drive but always worried. Keep them in different places and try to keep a copy of your photos on each. If one gets cracked, dunked, or pick pocketed you wont lose all your photos. If you can periodically upload some photos back to your family that will keep you from losing your mind if you get your entire bag swiped. A friend had his camera pulled out of his bag in Rome the last weekend of his trip and the only copy he had of the photos was on his memory card.

I did not bring a laptop. The boat I was working on had one I used to do simple transfers and uploads. When I returned home I did editing on my computer. You will need a way of transferring your photos to your external hard drives. There are internet cafe's you can use but it is nice to have your own laptop. Get something small and cheap ( Inspiron 11.6" Touch-Screen Laptop - AMD A6-Series - 4GB Memory - 500GB Hard Drive - Silver).

Take the 50mm f1.8 no matter what. It is cheap. Takes great photos and is light weight. It also makes the camera look less impressive then a long expensive zoom which is nice when you are walking around at night.

Buy locks for the zippers on your backpack and keep them locked at all times. Bring a purse, or small bag to take your camera and a spare lens if you need to leave your backpack at a hostel to do sightseeing.Bring one of your external hard drives with you if you are separated from your bag.